Wireless powering of devices by using radio-frequency (“RF”) signals (also referred to as “RF charging”) is a developing technology. Current RF charging systems 10, as illustrated in FIG. 1, typically have a power source 14 coupled to an RF transmitting antenna 18. The transmitting antenna 18 transmits RF energy 22 to a receiving antenna 26 of an electronic device 30. The receiving antenna 26 collects the RF energy, which is then transmitted to a RF-to-DC converter 34, which converts the energy into DC power for use in a load 38 of the device 30, for example a battery.
The prior art power transfer mechanism has been used in the past for long distance power transfer for sensors disposed in hard-to-wire areas, or for eliminating cables to enable easy and cheap installation. Such a power transfer mechanism has also been used in the past for RFID applications to read information from tags. However, electronic devices operating with prior art recharging systems require one antenna for communication and data signal transfer, and a separate antenna to receive the RF energy. Providing an electronic device with multiple antennas results in a bulky and more expensive electronic device.
Another known method for wirelessly recharging devices is referred to as “inductive power transfer.” Both the power source and the receiver need to have a coil attached. The power source delivers the power via coils. The device requires coils for recharging, which adds to hardware cost and increases the size of the devices. Moreover, inductive power transfer is sensitive to the relative orientation of the source coil and the receiver coil. High efficiency is achieved only when the two coils are properly aligned with respect to one another. Finally, inductive power transfer is only suitable for power transfer to a single device, since interference between devices has an adverse effect on transmission of inductive power to devices when there are multiple devices in close proximity to one another.
It would therefore be desirable to provide an improved power transmission and charging system for electronic devices.